Certain substituted 6,7-dihydro-1-oxo-1H,5H-benzo[ij]quinolizine-2-carboxylic acids are known to have antimicrobial activity and are disclosed in U.S. Pat. No. 3,896,131 (Gerster). Gerster discloses compounds substituted by halogen in the 8 or 9 position, but no compound substituted by halogen in both the 8 and 9 positions is described. It has now been found that certain compounds substituted by two different halogens in the 8 and 9 positions demonstrate greatly enhanced antimicrobial activity against certain key species of bacteria.
Specific compounds containing a halogen in the 8 or 9 position described by Gerster in the aforementioned patent include the 9-fluoro compound, the 8-chloro compound, the 9-chloro compound, the 10-chloro compound and the 9-bromo compound. Compounds substituted by halogen and one additional substituent in the 8 and 9 positions specifically disclosed by Gerster include: 8-chloro-9-methyl; 8-chloro-9-methoxy; 8-amino-9-chloro; and 8-acetamido-9-chloro. Compounds of the present invention exhibit greatly improved antimicrobial activity over the halogen-substituted compounds disclosed by Gerster.